There are two kinds of battery chargers, one is of linear type and the other is of switching type. FIG. 1 is a schematic diagram of a switching battery charger, and FIG. 2 is a schematic diagram of a linear battery charger.
In a switching battery charger, as shown in FIG. 1, an error amplifier 12 detects the output voltage VOUT at the power output terminal of the switching battery charger and the output current IOUT flowing through a current sense resistor RD to generate an error signal EA and according thereto, a pulse width modulation (PWM) controller 10 provides control signals PWM1 and PWM2 to switch a pair of upper bridge transistor 14 and lower bridge transistor 16, respectively, to convert an input voltage VIN received by a power input terminal of the switching battery charger into a current with an inductor L to supply the output current IOUT to charge a battery Bat at the power output terminal VOUT.
In a linear battery charger, as shown in FIG. 2, an error amplifier 22 detects the output voltage VOUT at the power output terminal of the linear battery charger to generate an error signal EA and according thereto, a linear controller 20 provides a control signal VG for controlling a transistor 24 to supply an output current IOUT to charge a battery Bat at the power output terminal VOUT.
These two kinds of battery chargers have respective advantages and disadvantages. The linear battery charger is a simple solution but will suffer poor efficiency issue; while the switching battery charger has better efficiency but will suffer electromagnetic interference (EMI) issue. Therefore, designers always select either one of them for applications depending on the practical demands of circuits.